ci: add Gitea Actions workflow and unit tests

- Add .gitea/workflows/ci.yml: runs build + tests on push/PR to main
- Add vitest as dev dependency
- Add src/utils.test.ts: 4 tests covering handleTool success, Error throw,
  non-Error throw, and arg passthrough
- Add src/client.test.ts: 12 tests covering URL building, Authorization header,
  query string params, Content-Type presence/absence, error handling with
  message extraction and statusText fallback, and HTTP method correctness

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: CI
+
+on:
+    push:
+        branches: ["main"]
+    pull_request:
+        branches: ["main"]
+
+jobs:
+    ci:
+        name: Build & Test
+        runs-on: ubuntu-latest
+
+        steps:
+            - name: Checkout repository
+              uses: actions/checkout@v4
+
+            - name: Install pnpm
+              uses: pnpm/action-setup@v6
+
+            - name: Setup Node.js
+              uses: actions/setup-node@v4
+              with:
+                  node-version: "22"
+                  cache: "pnpm"
+
+            - name: Install dependencies
+              run: pnpm install
+
+            - name: Build
+              run: pnpm build
+
+            - name: Test
+              run: pnpm test